Mars is a world of giants. Its dusty orange surface is dotted by some of the biggest volcanic mountains in the solar system. They built up over thousands of years as molten rock gently bubbled to the surface.
Three of the five largest volcanoes are in a region known as Tharsis, while a fourth — the tallest of all — is just on its edge. All of these mountains are miles taller than Mount Everest. Yet for the most part, their slopes are gentle.
The biggest of the bunch is Olympus Mons, the tallest volcano in the solar system. It’s more than 13 miles high, and covers an area bigger than most American states. The crater at its summit is so wide that if you stood at its rim, you couldn’t see the other side. And although most of its slope is gentle, its edge is marked by tall, sharp cliffs.
The volcanoes grew so tall and wide because the lava that poured out of them was fairly thin and runny. It spread out easily, covering large areas of the surface. Many volcanoes on Earth are built by thicker lava, which hardens quickly. That allows pressure to build up from below, eventually causing an explosion.
Today, the Martian volcanoes all appear to be dormant and perhaps extinct — they haven’t staged any large-scale activity in a long time. Yet they continue to tower above the dusty plains of Mars.
Look for Mars to the upper left of the Moon as they rise late this evening. The planet looks like a bright orange star.
Script by Damond Benningfield, Copyright 2011